[derive] Support deriving NoCell

Makes progress on #251

src/byteorder.rs

@@ -276,7 +276,7 @@ example of how it can be used for parsing UDP packets.
 [`AsBytes`]: crate::AsBytes
 [`Unaligned`]: crate::Unaligned"),
             #[derive(Copy, Clone, Eq, PartialEq, Hash)]
-            #[cfg_attr(any(feature = "derive", test), derive(KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned))]
+            #[cfg_attr(any(feature = "derive", test), derive(KnownLayout, NoCell, FromZeroes, FromBytes, AsBytes, Unaligned))]
             #[repr(transparent)]
             pub struct $name<O>([u8; $bytes], PhantomData<O>);
         }
@@ -288,7 +288,9 @@ example of how it can be used for parsing UDP packets.
             /// SAFETY:
             /// `$name<O>` is `repr(transparent)`, and so it has the same layout
             /// as its only non-zero field, which is a `u8` array. `u8` arrays
-            /// are `FromZeroes`, `FromBytes`, `AsBytes`, and `Unaligned`.
+            /// are `NoCell`, `FromZeroes`, `FromBytes`, `AsBytes`, and
+            /// `Unaligned`.
+            impl_or_verify!(O => NoCell for $name<O>);
             impl_or_verify!(O => FromZeroes for $name<O>);
             impl_or_verify!(O => FromBytes for $name<O>);
             impl_or_verify!(O => AsBytes for $name<O>);

src/lib.rs

@@ -264,6 +264,14 @@ pub use zerocopy_derive::Unaligned;
 #[doc(hidden)]
 pub use zerocopy_derive::KnownLayout;
 
+// `pub use` separately here so that we can mark it `#[doc(hidden)]`.
+//
+// TODO(#251): Remove this or add a doc comment.
+#[cfg(any(feature = "derive", test))]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
+#[doc(hidden)]
+pub use zerocopy_derive::NoCell;
+
 use core::{
     cell::{self, RefMut},
     cmp::Ordering,
@@ -7921,7 +7929,7 @@ mod tests {
         assert_impls!(Wrapping<NotZerocopy>: KnownLayout, !NoCell, !TryFromBytes, !FromZeroes, !FromBytes, !AsBytes, !Unaligned);
         assert_impls!(Wrapping<UnsafeCell<()>>: KnownLayout, !NoCell, !TryFromBytes, !FromZeroes, !FromBytes, !AsBytes, !Unaligned);
 
-        assert_impls!(Unalign<u8>: KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned, !NoCell, !TryFromBytes);
+        assert_impls!(Unalign<u8>: KnownLayout, NoCell, FromZeroes, FromBytes, AsBytes, Unaligned, !TryFromBytes);
         assert_impls!(Unalign<NotZerocopy>: Unaligned, !NoCell, !KnownLayout, !TryFromBytes, !FromZeroes, !FromBytes, !AsBytes);
 
         assert_impls!([u8]: KnownLayout, NoCell, FromZeroes, FromBytes, AsBytes, Unaligned, !TryFromBytes);

src/util.rs

@@ -616,6 +616,7 @@ pub(crate) mod testutil {
     // By contrast, `AU64` is guaranteed to have alignment 8.
     #[derive(
         KnownLayout,
+        NoCell,
         FromZeroes,
         FromBytes,
         AsBytes,
@@ -645,7 +646,7 @@ pub(crate) mod testutil {
     }
 
     #[derive(
-        FromZeroes, FromBytes, Eq, PartialEq, Ord, PartialOrd, Default, Debug, Copy, Clone,
+        NoCell, FromZeroes, FromBytes, Eq, PartialEq, Ord, PartialOrd, Default, Debug, Copy, Clone,
     )]
     #[repr(C)]
     pub(crate) struct Nested<T, U: ?Sized> {

src/wrappers.rs

@@ -60,7 +60,7 @@ use super::*;
 #[derive(Default, Copy)]
 #[cfg_attr(
     any(feature = "derive", test),
-    derive(KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned)
+    derive(NoCell, KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned)
 )]
 #[repr(C, packed)]
 pub struct Unalign<T>(T);
@@ -74,7 +74,10 @@ safety_comment! {
     ///   alignment of `T`, and so we don't require that `T: Unaligned`
     /// - `Unalign<T>` has the same bit validity as `T`, and so it is
     ///   `FromZeroes`, `FromBytes`, or `AsBytes` exactly when `T` is as well.
+    /// - `NoCell`: `Unalign<T>` has the same fields as `T`, so it contains
+    ///   `UnsafeCell`s exactly when `T` does.
     impl_or_verify!(T => Unaligned for Unalign<T>);
+    impl_or_verify!(T: NoCell => NoCell for Unalign<T>);
     impl_or_verify!(T: FromZeroes => FromZeroes for Unalign<T>);
     impl_or_verify!(T: FromBytes => FromBytes for Unalign<T>);
     impl_or_verify!(T: AsBytes => AsBytes for Unalign<T>);

zerocopy-derive/src/lib.rs

@@ -243,6 +243,23 @@ pub fn derive_known_layout(ts: proc_macro::TokenStream) -> proc_macro::TokenStre
     .into()
 }
 
+#[proc_macro_derive(NoCell)]
+pub fn derive_no_cell(ts: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    let ast = syn::parse_macro_input!(ts as DeriveInput);
+    match &ast.data {
+        Data::Struct(strct) => {
+            impl_block(&ast, strct, Trait::NoCell, RequireBoundedFields::Yes, false, None, None)
+        }
+        Data::Enum(enm) => {
+            impl_block(&ast, enm, Trait::NoCell, RequireBoundedFields::Yes, false, None, None)
+        }
+        Data::Union(unn) => {
+            impl_block(&ast, unn, Trait::NoCell, RequireBoundedFields::Yes, false, None, None)
+        }
+    }
+    .into()
+}
+
 #[proc_macro_derive(FromZeroes)]
 pub fn derive_from_zeroes(ts: proc_macro::TokenStream) -> proc_macro::TokenStream {
     let ast = syn::parse_macro_input!(ts as DeriveInput);
@@ -637,6 +654,7 @@ impl PaddingCheck {
 #[derive(Debug, Eq, PartialEq)]
 enum Trait {
     KnownLayout,
+    NoCell,
     FromZeroes,
     FromBytes,
     AsBytes,

zerocopy-derive/tests/ui-msrv/enum.stderr

@@ -31,149 +31,149 @@ error: must have a non-align #[repr(...)] attribute in order to guarantee this t
    = note: this error originates in the derive macro `FromBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: only C-like enums can implement FromZeroes
-  --> tests/ui-msrv/enum.rs:52:1
+  --> tests/ui-msrv/enum.rs:61:1
    |
-52 | / enum FromZeroes1 {
-53 | |     A(u8),
-54 | | }
+61 | / enum FromZeroes1 {
+62 | |     A(u8),
+63 | | }
    | |_^
 
 error: only C-like enums can implement FromZeroes
-  --> tests/ui-msrv/enum.rs:57:1
+  --> tests/ui-msrv/enum.rs:66:1
    |
-57 | / enum FromZeroes2 {
-58 | |     A,
-59 | |     B(u8),
-60 | | }
+66 | / enum FromZeroes2 {
+67 | |     A,
+68 | |     B(u8),
+69 | | }
    | |_^
 
 error: FromZeroes only supported on enums with a variant that has a discriminant of `0`
-  --> tests/ui-msrv/enum.rs:63:1
+  --> tests/ui-msrv/enum.rs:72:1
    |
-63 | / enum FromZeroes3 {
-64 | |     A = 1,
-65 | |     B,
-66 | | }
+72 | / enum FromZeroes3 {
+73 | |     A = 1,
+74 | |     B,
+75 | | }
    | |_^
 
 error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
-  --> tests/ui-msrv/enum.rs:73:8
+  --> tests/ui-msrv/enum.rs:82:8
    |
-73 | #[repr(C)]
+82 | #[repr(C)]
    |        ^
 
 error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
-  --> tests/ui-msrv/enum.rs:79:8
+  --> tests/ui-msrv/enum.rs:88:8
    |
-79 | #[repr(usize)]
+88 | #[repr(usize)]
    |        ^^^^^
 
 error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
-  --> tests/ui-msrv/enum.rs:85:8
+  --> tests/ui-msrv/enum.rs:94:8
    |
-85 | #[repr(isize)]
+94 | #[repr(isize)]
    |        ^^^^^
 
 error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
-  --> tests/ui-msrv/enum.rs:91:8
-   |
-91 | #[repr(u32)]
-   |        ^^^
+   --> tests/ui-msrv/enum.rs:100:8
+    |
+100 | #[repr(u32)]
+    |        ^^^
 
 error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
-  --> tests/ui-msrv/enum.rs:97:8
-   |
-97 | #[repr(i32)]
-   |        ^^^
+   --> tests/ui-msrv/enum.rs:106:8
+    |
+106 | #[repr(i32)]
+    |        ^^^
 
 error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
-   --> tests/ui-msrv/enum.rs:103:8
+   --> tests/ui-msrv/enum.rs:112:8
     |
-103 | #[repr(u64)]
+112 | #[repr(u64)]
     |        ^^^
 
 error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
-   --> tests/ui-msrv/enum.rs:109:8
+   --> tests/ui-msrv/enum.rs:118:8
     |
-109 | #[repr(i64)]
+118 | #[repr(i64)]
     |        ^^^
 
 error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
-   --> tests/ui-msrv/enum.rs:119:8
+   --> tests/ui-msrv/enum.rs:128:8
     |
-119 | #[repr(C)]
+128 | #[repr(C)]
     |        ^
 
 error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
-   --> tests/ui-msrv/enum.rs:125:8
+   --> tests/ui-msrv/enum.rs:134:8
     |
-125 | #[repr(u16)]
+134 | #[repr(u16)]
     |        ^^^
 
 error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
-   --> tests/ui-msrv/enum.rs:131:8
+   --> tests/ui-msrv/enum.rs:140:8
     |
-131 | #[repr(i16)]
+140 | #[repr(i16)]
     |        ^^^
 
 error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
-   --> tests/ui-msrv/enum.rs:137:8
+   --> tests/ui-msrv/enum.rs:146:8
     |
-137 | #[repr(u32)]
+146 | #[repr(u32)]
     |        ^^^
 
 error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
-   --> tests/ui-msrv/enum.rs:143:8
+   --> tests/ui-msrv/enum.rs:152:8
     |
-143 | #[repr(i32)]
+152 | #[repr(i32)]
     |        ^^^
 
 error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
-   --> tests/ui-msrv/enum.rs:149:8
+   --> tests/ui-msrv/enum.rs:158:8
     |
-149 | #[repr(u64)]
+158 | #[repr(u64)]
     |        ^^^
 
 error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
-   --> tests/ui-msrv/enum.rs:155:8
+   --> tests/ui-msrv/enum.rs:164:8
     |
-155 | #[repr(i64)]
+164 | #[repr(i64)]
     |        ^^^
 
 error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
-   --> tests/ui-msrv/enum.rs:161:8
+   --> tests/ui-msrv/enum.rs:170:8
     |
-161 | #[repr(usize)]
+170 | #[repr(usize)]
     |        ^^^^^
 
 error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
-   --> tests/ui-msrv/enum.rs:167:8
+   --> tests/ui-msrv/enum.rs:176:8
     |
-167 | #[repr(isize)]
+176 | #[repr(isize)]
     |        ^^^^^
 
 error: cannot derive Unaligned with repr(align(N > 1))
-   --> tests/ui-msrv/enum.rs:173:12
+   --> tests/ui-msrv/enum.rs:182:12
     |
-173 | #[repr(u8, align(2))]
+182 | #[repr(u8, align(2))]
     |            ^^^^^^^^
 
 error: cannot derive Unaligned with repr(align(N > 1))
-   --> tests/ui-msrv/enum.rs:179:12
+   --> tests/ui-msrv/enum.rs:188:12
     |
-179 | #[repr(i8, align(2))]
+188 | #[repr(i8, align(2))]
     |            ^^^^^^^^
 
 error: cannot derive Unaligned with repr(align(N > 1))
-   --> tests/ui-msrv/enum.rs:185:18
+   --> tests/ui-msrv/enum.rs:194:18
     |
-185 | #[repr(align(1), align(2))]
+194 | #[repr(align(1), align(2))]
     |                  ^^^^^^^^
 
 error: cannot derive Unaligned with repr(align(N > 1))
-   --> tests/ui-msrv/enum.rs:191:8
+   --> tests/ui-msrv/enum.rs:200:8
     |
-191 | #[repr(align(2), align(4))]
+200 | #[repr(align(2), align(4))]
     |        ^^^^^^^^
 
 error[E0565]: meta item in `repr` must be an identifier
@@ -197,3 +197,12 @@ error[E0566]: conflicting representation hints
    = note: `#[deny(conflicting_repr_hints)]` on by default
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
+
+error[E0277]: the trait bound `UnsafeCell<()>: NoCell` is not satisfied
+  --> tests/ui-msrv/enum.rs:51:10
+   |
+51 | #[derive(NoCell)]
+   |          ^^^^^^ the trait `NoCell` is not implemented for `UnsafeCell<()>`
+   |
+   = help: see issue #48214
+   = note: this error originates in the derive macro `NoCell` (in Nightly builds, run with -Z macro-backtrace for more info)